Here is an adaptation of Paul's code that should work with a named autotext entry stored in the document's attached template:
Code:
Private Sub CheckBox1_Click()
If CheckBox1.Value = True Then
Call UpdateBookmark("Destination", "ATEntry" & vbCr)
Else
Call UpdateBookmark("Destination")
End If
End Sub
Sub UpdateBookmark(BmkNm As String, Optional strATName As String)
Dim BmkRng As Range
With ActiveDocument
If .Bookmarks.Exists(BmkNm) Then
Set BmkRng = .Bookmarks(BmkNm).Range
If strATName <> vbNullString Then
Set BmkRng = ActiveDocument.AttachedTemplate.AutoTextEntries(strATName).Insert(Where:=BmkRng)
Else
BmkRng.Text = vbNullString
End If
.Bookmarks.Add BmkNm, BmkRng
End If
End With
Set BmkRng = Nothing
End Sub